On the final Saturday of the regular season, Johnny Football will become Johnny Spectator. A week later, I fully expect Texas A&M’s freshman quarterback to then become Johnny Heisman.

I can’t imagine anything that could derail Johnny Manziel as he and the rest of the Aggies sit back and watch the developments. His biggest competition appears to come from Notre Dame linebacker Manti Te’o, although I think his chances could be damaged Saturday without the Irish even taking the field.

The only true Heisman candidate in action is Kansas State quarterback Collin Klein as the Wildcats host Texas.

I will admit I have come full circle on Klein. When he was the Heisman front-runner about six weeks ago, I was reluctant to think I would be voting for a quarterback with such an awkward throwing motion. We’re not talking about Tim Tebow’s slow delivery at Florida or anything of that nature. We’re talking about absolute amazement that Klein ever completes a pass 20 yards downfield.

But now I have gone the other direction. Call it the R.A. Dickey factor. If a major league pitcher can win 20 games and compile the kind of walk-strikeout ratio that the Mets ace did while throwing a knuckleball?

Just give him the Cy Young hardware.

And if Klein can lead Kansas State to a Big 12 title and complete 67 percent of his passes for respectable yardage with that motion, he has to get consideration. But I think the three-interception night in Baylor, which doubled his season total and dropped the Wildcats from the No. 1 ranking, will keep Klein from finishing higher than third on most ballots.

Manziel’s ascent to the top spot has had as much to do with the failings of others as his own improbable rise. This was Matt Barkley’s Heisman to lose at USC when the season began. But unburdened from the shackles of probation, we saw how Barkley and the Trojans responded to freedom. They fell apart.

Then it was Geno Smith’s turn at West Virginia. When the Mountaineers beat Texas to run their record to 5-0, Smith had 24 TD passes and no interceptions. You can’t help but capture the Heisman if you stay on that pace but, of course, Smith and West Virginia did not. He had 13 TD passes and five interceptions as West Virginia lost five straight before finishing with a win at Iowa State.

With no running backs taking center stage, the door was open for an unlikely freshman. Manziel made an immediate impact, even in the opening loss to Florida. He set the SEC total offense record in his fourth start against Arkansas and broke it two weeks later in a nonconference win against a ranked Louisiana Tech team.

It was in watching the second half of that Louisiana Tech game that I first began to think, “Is this guy going to be one of the three names on my Heisman ballot?” But the history of freshmen — in particular freshman quarterbacks — made it seem too fantastic, even as Manziel was stepping over the candidates tripping in front of him.

I think a lot of Heisman voters wish he had had a better game against LSU. He threw three of his eight interceptions that afternoon and scored none of his 43 rushing and passing touchdowns.

But the Aggies’ upset in Alabama remains the most memorable game of the 2012 season, and the nation’s voters saw Manziel scrambling to make plays throughout the contest and exhorting his teammates on the bench between series.

That left no doubt that Manziel was in contention, and as he moved past the Heisman numbers compiled by Tebow and Auburn’s Cam Newton (except won-loss record, no small consideration), he became the odds-on favorite.

The national groundswell for Te’o is difficult to gauge. The Fighting Irish deserve the No. 1 ranking, but voting for a linebacker is as much a guess as anything else. With the statistics on quarterbacks and running backs, we can compare players not only within a season but with past winners as well.

Te’o has the interceptions and he has the leadership skills and the narrative. But is he truly better than Georgia linebacker Jarvis Jones? I think a big afternoon from Jones on Saturday against Alabama will actually hurt the chances of Te’o and give Manziel the final push he needs to become the first freshman Heisman winner.